1. Technical Field
Embodiments of the subject matter disclosed herein generally relate to methods and systems and, more particularly, to mechanisms and techniques for reducing a stroke of a ram block in a ram blowout preventer.
2. Discussion of the Background
During the past years, with the increase in price of fossil fuels, the interest in developing new production fields has increased dramatically. However, the availability of land-based production fields is limited. Thus, the industry has now extended drilling to offshore locations, which appear to hold a vast amount of fossil fuel.
The existing technologies for extracting the fossil fuel from offshore fields use a system 10 as shown in FIG. 1. More specifically, the system 10 includes a vessel 12 having a reel 14 that supplies power/communication cords 16 to a controller 18. The controller 18 is disposed undersea, close to or on the seabed 20. In this respect, it is noted that the elements shown in FIG. 1 are not drawn to scale and no dimensions should be inferred from FIG. 1.
FIG. 1 also shows a wellhead 22 of the subsea well and a drill line 24 that enters the subsea well. At the end of the drill line 24 there is a drill (not shown). Various mechanisms, also not shown, are employed to rotate the drill line 24, and implicitly the drill, to extend the subsea well.
However, during normal drilling operation, unexpected events may occur that could damage the well and/or the equipment used for drilling. One such event is the uncontrolled flow of gas, oil or other well fluids from an underground formation into the well. Such event is sometimes referred to as a “kick” or a “blowout” and may occur when formation pressure inside the well exceeds the pressure applied to it by the column of drilling fluid. This event is unforeseeable and if no measures are taken to prevent it, the well and/or the associated equipment may be damaged. Although the above discussion was directed to subsea oil exploration, the same is true for ground oil exploration.
Thus, a blowout preventer (BOP) might be installed on top of the well to seal the well in case that one of the above mentioned events is threatening the integrity of the well. The BOP is conventionally implemented as a valve to prevent the release of pressure either in the annular space between the casing and the drill pipe or in the open hole (i.e., hole with no drill pipe) during drilling or completion operations. Recently, a plurality of BOPs may be installed on top of the well for various reasons. FIG. 1 shows two BOPs 26 or 28 that are controlled by the controller 18.
A traditional BOP may be one to five meters high and may weight tens of thousands of kilograms. Various components of the BOP need to be replaced from time to time. An example of a BOP 26 is shown in FIG. 2. The BOP 26 shown in FIG. 2 has, among other things, two ram blocks 30 that are supported by respective piston rods 32 and a corresponding locking mechanism 33, which is configured to lock the rods 32 at desired positions. The two ram blocks 30 are configured to move inside a first chamber 34 (horizontal bore) along a direction parallel to a longitudinal axis X of the piston rods 32. The ram blocks 30 may severe the drill line 24 or other tools that cross a second chamber 36 (vertical wellbore) of the BOP 26. First and second chambers are substantially perpendicular to each other. However, after cutting the drill line 24 for a number of times (if a shear ram block is installed), the ram blocks 30 and/or their respective cutting edges need to be verified and sometimes reworked. For this reason, the BOP 26 of FIG. 2 is provided with a removable bonnet 38, for each ram block 30, which can be opened for providing access to the ram blocks. FIG. 2 shows the bonnet 38 having a hinge 40 that rotatably opens the bonnet 38.
FIG. 3 shows the BOP 26 having the bonnet 38 opened so as to expose the ram block 30. Thus, in order to perform maintenance on the ram block 30, the bonnet 38 needs to be opened while the ram block 30 is placed at a certain position, so that the bonnet may open freely without interfering with BOP 26. This specific position of the ram block 30 that allows the bonnet 38 to open does not coincide with a functional open position of the ram block, i.e., a position that allows tools to enter through the second chamber 36. The specific position of the ram block 30 corresponds to the ram block being further withdrawn inside the bonnet 38 as the ram block needs to swing with the bonnet 38 around hinge 40 without touching a side 42a of a body 42 of the BOP 26. In other words, the ram block 30 may have a functional open position when the bonnet 38 is closed and the ram block is operational and a maintenance open position when the bonnet 38 has to be opened. These two positions do not coincide for the traditional BOPs. The traditional BOPs are using the maintenance opened position for both when the ram block is operational and when the bonnet has to be opened. This design is making the BOPs to use a fluid under pressure (for opening/closing the ram blocks) more than necessary.
Therefore, it is desired to provide a novel BOP that uses the correct amount of fluid under pressure, which makes the operation of the BOP faster and more cost-effective.